Magnetic circuit for the deflection of flux leakage



y 1964 TOSHIHIKO TSUNOO ETAL 3,134,057

MAGNETIC CIRCUIT FOR THE DEFLECTION OF FLUX LEAKAGE Filed Sept. 21, 19602 Sheets-Sheet 1 y 1964 TOSHIHIKO TSUNOO ETAL 3,134,057

v MAGNETIC CIRCUIT F OR THE DEFLECTION OF FLUX LEAKAGE Filed Sept. 21,1960 2Sheets-Sheet 2 45 40 A M 4% H54.

:15 40 5 AZ: 4 41 54 F/5 5 164mg 41 4 F/5 5 114 United States Patent3,134,057 MAGNETIC CIRCUIT FOR THE DEFLECTION GF FLUX LEAKAGE ToshihikoTsunoo, Amagasaki-shi, and Mitsno Uruma,

Nishinomiya-shi, Japan, assignors to Sunnitomo Kinzoku Kogyo KahushikiKaisha, Osaka-shi, Japan, a corporation of Japan Filed Sept. 21, 1960,fier. No. 57,488 Claims priority, application Japan July 11, 1960Claims. (CL 317-201) This invention relates to a magnetic circuitwherein a small vacant space or a thin non-magnetic material is providedon a permanent magnet, an electromagnet, a yoke or a pole piece at itsend face where magnetic fluX leakage occurs, in such a manner that amagnetic pole stands opposite to said end face in the same polaritythereby causing the magnetic pole to repulse and then deflect leakageflux toward the opposite pole of an effective air gap and thus toincrease the flux in the air gap.

Magnetic circuits of the type in which a permanent magnet or anelectromagnet is used are, in general, arranged to utilize the magneticflux induced from the two poles of said magnet or accumulated in an airgap through a pole piece or a yoke of soft magnetic material such assoft iron. The magnetic circuit of such type has some disadvantages asdescribed hereinafter.

The nature of the present invention and its advantages will be fullyunderstood from the following description with reference to theaccompanying drawings, in which:

FIG. 1 is a cross-sectional view showing, by way of example, aconventional magnetic circuit;

FIG. 2 is a similar view showing one embodiment of the presentinvention;

FIG. 3 illustrates a cross-section of a permanent magnet speakerassembly wherein the magnetic circuit accord ing to the presentinvention is incorporated;

FIG. 4 is a cross-sectional side view showing the known magnet rollerfor pressing and drafting;

FIG. 5 is a similar view showing the magnet roller to which the magneticcircuit of the present invention is applied;

FIG. 6 is another similar view showing a part of a modified form of thesame.

Referring now to FIG. 1, the conventional magnet circuit generally usedfor the permanent magnet speaker assembly with a central pillar typemagnet comprises a permanent magnet 1, a pole piece 2, a yoke 3 and anannular air gap 4 formed by said pole piece and the yoke, in which gapthe flux is-introducedfrom the permanent magnet and accumulated for use.Such magnetic circuit of prior art has a-defect in that a desiredaccumulation of the effective flux inthe air gap is prevented due tofiuX leakage from the end face of permanent magnet, electromagnet, yokeor pole piece. In the known circuit shown in FIG. 1, the flux induced bythe pole piece 2 is deflected 90 at the end face thereof and attractedtowards the yoke 3 through the air gap 4 but at the same time aconsiderable amount of flux is not bent as desired and leaks upwardlyfrom the end face of the pole piece 2. Thus, for making effective use ofthe flux through the air gap in the magnetic circuit, it is necessary toreduce leakage of the flux in transit to a minimum.

In FIGS. 2 and 3 illustrating the same speaker assembly as in FIG. 1, amagnetic circuit according to the present invention comprises apermanent magnet 1, a pole piece 2, a yoke 3 and air gap 4. On the topend face of the pole piece 2 a non-magnetic material 5 like Bakelite isplaced, and a high coercivity permanent magnet 6 such as barium ferritemagnet is so disposed upon said material 5 that its side facing the polepiece 2 becomes the same polarity therewith. Instead of placing saidmamagnetic performance.

terial 5, that place may be used as a vacant space (FIG. 3). In FIG. 3,7 is a voice coil, 8 a cone paper, 9 a damper and 10 a frame.

In operation, the flux liable to leak upwardly from the top end face ofthe pole piece 2 is repulsed by the flux of the magnet 6 owing to thesame polarity, and attracted to the opposite polarity of the yoke 3 toaccumulate into the air gap 4 thereby increasing the gap flux density.In addition, the flux of the magnet 6 facing the pole piece 2 is alsodrawn into the air gap 4. Thus, by these two processes, the gapfluxdensity is increased 10-20% compared with the arrangement shown in FIG.1.

As a magnetic pole having the same polarity confronting the end face ofthe magnet 6 where flux leakage occurs, there may be used a highcoercivity permanent magnet 6 such as barium ferrite magnet,manganese-bismuthic magnet and alnico magnet. Even a thin plate magnetof the above type can be employed without any loss of For instance, suchplate magnet is used in the magnetic circuit for a loudspeaker withadvantage that due to its flatness it is conveniently embraced in themoving coil part of the cone paper. As a permanent magnet 1 in the basecircuit there is no need for a high coercivity permanent magnet to use,since the magnetic circuit consisting of magnet 1, pole piece 2 and yoke3 forms practically a closed magnetic circuit so that the magneticperformance of the circuit is not decreased even in the state ofrepulsion between the magnetic poles of magnets 6 and 1.

The following Table 1 shows the gap flux density in the magnetic circuitaccording to the present invention as illustrated in FIG. 2 comparedwith that in the known circuit (FIG. 1).

wherein the permanent magnet 1 used in the circuit I was a bottle-shapedalnico casting magnet of 17.5 mm. 4: X 13 mm. 4) X 14 mm., while thatused in the circuit II was a pillar-shaped alnico casting magnet of 13mm. x 12 mm. The gap length in both circuits was 0.55 mm. The permanentmagnet 6 used in the circuit II was a barium ferrite magnet of 13 mm.(1; X 3 mm. The non-magnetic material 5 used was a Bakelite disc.

As clearly seen from the above table, the gap flux density in themagnetic circuit according to the present invention is much larger thanthat in prior art.

We have now particularly described an embodiment of the presentinvention applying to the magnetic circuit using a central pillar typemagnet wherein the leakage flux from the end face of the pole piece 2 isrepulsed so as to increase the flux in the air gap 4.

Same advantage can be obtained in a similar magnetic circuit using amagnet without a pole piece by disposing a small vacant space or a thinplate of non-magnetic material immediately on the end face of the magnetin such a manner that the same polarities of the magnet and anothermagnet or its magnetizing coil are facing each other. Also in a magneticcircuit using a ring type magnet or in the base circuit using anelectromagnet in place of a permanent magnet, a good magnetic circuitcan be easily obtained in similar way.

Another embodiment of the present invention is shown by applying tomagnetically attractive rollers generally used for pressing and draftingof fibers, paper and film.

Referring to FIG. 4 illustrating a typical magnetic circuit in the knownmagnet roller, the roller comprises a permanent magnet 1 having poles inthe axial direction, a

yoke 3 connecting to each pole of the magnet 1, an outer casing 11 ofnon-magnetic material which incorporates the magnet 1 and the yoke 3into one body, a cot 12, a pole ring 13, said cot and pole ring beingput respectively on the round pillar side of the yoke 3, and anon-magnetic cap 14 fitted on the shaft of the yoke 3. The magneticcircuit is formed by a magnetically inductive roller 15 such as a flutedroller cooperating with the magnet roller, thus both rollers beingattracted to each other through the .fiux in an air gap'4'therebetween.This circuit however has defect that a considerable amount of magneticflux leaksfrom; the axial end face of the magnet roller therebydecreasing the flux in the effective air gap and intensifyingmagnetization around the shaft of the magnet roller.

As shown in FIG. 5, in the magnetic circuit according to the presentinvention for the magnet roller having the same structure with thatshown in FIG. 4, a high coercivity magnet piece 6 such as barium ferritemagnet is fitted .on the axial end face of the pole ring 13 in such away that the same polarities are facing each other in order to is soarranged as to leave a space between the end face of the pole ring 13and the opposing magnet piece 6 of high coercivity. The separator isformed of a flange portion 16 of the non-magnetic cap 14 covering theaxial end face of the pole ring 13. Instead of the arrangement that thesame polarities stand close to each other as shown in FIG. 5, there isthus provided a proper space between the same polarities so that theflux from the permanent magnet 1 is more advantageously repulsed andeffectively deflected into the air gap 4.

Tests of the magnetic circuit were conducted on a magnet roller of 28mm. in outer diameter and 126 mm. in length wherein a permanent magnetof 25 mm. in outer diameter and 50 mm. in length (l3 13,500 gausses, H650 oersteds) and as a pole piece forming the air gap, a pole ring of27.6 mm. in outer diameter, 18 mm. in inner diameter and 8 mm. in lengthwere used. The result was that the attractive power was 7.2 kg. on thefluted roller in the magnetic circuit shown in FIG. 4, while on theother hand, in the magnetic circuit shown in FIG. 5 wherein a highcoercivity magnet piece of 27 mm. in outer diameter, 17 mm. in width and3 mm. in length (B 3,500 gausses, H

4 2,800 oersteds) was fitted, the attractive power was 8.3 kg., 15%higher than in FIG. 4.

The present invention provides a magnetic circuit which excels as oneused for loudspeakers and magnet rollers, and also for acousticmachines, meters and vibrators.

We claim:

1. A magnetic circuit comprising: an axially polarized central magnet,including first and second end portions; a magnetic pole piece incontact with one end portion of said central magnet and axiallyextending therefrom; a yoke including a central portion in contact withthe second end portion of said central magnet, a side portion spacedfrom and extending parallel to said central magnet and said magneticpole piece, and a top portion extending laterally toward said magneticpole piece to provide an annular gap between the top portion of saidyoke and said magnetic pole piece; a second magnet of high coercivityaxially displaced from said magnetic pole piece to provide a second gapbetween said magnetic pole piece and said second magnet, said secondmagnet being magnetically polarized with respect to the polarization ofsaid first magnet to force the leakage flux in said second gap from saidcentral magnet to the top portion of said yoke via said annular gap.

2. The magnetic circuit of claim 1, wherein said first magnet is apermanent magnet.

3. The magnetic circuit of claim 1 including a spacer of non-magneticmaterial interposed between said magnetic pole piece and said secondmagnet to define said second gap. 7

4. The magnetic circuit of claim 1 including a voice coil disposed aboutsaid magnetic pole piece and a cone fixed to said voice coil.

5. A magnetic roller comprising a cylindrical magnet which is axiallypolarized, cylindrical yokes fixed to each end of said cylindricalmagnet, annular pole rings fixed to said cylindrical yokes and havingdiameters less than said cylindrical yokes, a magnetically inductiveroller including an outer surface disposed parallel and adjacent theperipheral surfaces of said cylindrical magnet, said cylindrical yokesand said annular pole pieces whereby a material to be rolled isinsertable in the gap between said outer surface and said peripheralsurfaces, magnet pieces having high coercivity fixed to said annularpole rings, said magnetic pieces being polarized with respect to saidcylindrical magnet to force the axial flux from the ends of said annularpole rings radially toward said magnetically inductive roller.

References Cited in the file of this patent 7 UNITED STATES PATENTS2,585,714 Wrobel et al Feb. 12, 1952 2,698,917 Van Urk et al Jan. 4,1955 2,895,092 Cluwen July 14, 1959 2,993,152 Pierce et al July 18, 19613,067,366 Hofman Dec. 4, 1962 FOREIGN PATENTS 670,667 Great Britain Apr.23, 1952

1. A MAGNETIC CIRCUIT COMPRISING: AN AXIALLY POLARIZED CENTRAL MAGNET,INCLUDING FIRST AND SECOND END PORTIONS; A MAGNETIC POLE PIECE INCONTACT WITH ONE END PORTION OF SAID CENTRAL MAGNET AND AXIALLYEXTENDING THEREFROM; A YOKE INCLUDING A CENTRAL PORTION IN CONTACT WITHTHE SECOND END PORTION OF SAID CENTRAL MAGNET, A SIDE PORTION SPACEDFROM AND EXTENDING PARALLEL TO SAID CENTRAL MAGNET AND SAID MAGNETICPOLE PIECE, AND A TOP PORTION EXTENDING LATERALLY TOWARD SAID MAGNETICPOLE PIECE TO PROVIDE AN ANNULAR GAP BETWEEN THE TOP PORTION OF SAIDYOKE AND SAID MAGNETIC POLE PIECE; A SECOND MAGNET OF HIGH COERCIVITYAXIALLY DISPLACED FROM SAID MAGNETIC POLE PIECE TO PROVIDE A SECOND GAPBETWEEN SAID MAGNETIC POLE PIECE AND SAID SECOND MAGNET, SAID SECONDMAGNET BEING MAGNETICALLY POLARIZED WITH RESPECT TO THE POLARIZATION OFSAID FIRST MAGNET TO FORCE THE LEAKAGE FLUX IN SAID SECOND GAP FROM SAIDCENTRAL MAGNET TO THE TOP PORTION OF SAID YOKE VIA SAID ANNULAR GAP.